This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are using X-ray crystallography studies of a Ca2+ activated K+ channel, called MthK, in order to understand better the mechanisms of channel activation upon the binding of Ca2+, the gating process conformational change, and the K+ conduction process. We are also crystallizing another ligand gated channel that binds cyclic nucleotide molecules in order to open and close. The structural data will increase our understanding of how ligand binding regulates the gating mechanism of the ion channel pore.